Niacin and vitamin B6 in mental functioning: a review of controlled trials in humans.

Fifty-three controlled trials of the effects of niacin, vitamin B6, and multivitamins on mental functions are reviewed. The results are interpreted with emphasis on the methodological quality of the trials. It turns out that virtually all trials show serious short-comings: in the number of participants, the presentation of baseline characteristics and outcomes, and the description of changes in concomitant treatments. Only in autistic children are some positive results are found with very high dosages of vitamin B6 combined with magnesium, but further evidence is needed before more definitive conclusions can be drawn. For many other indications (hyperactive children, children with Down's syndrome, IQ changes in healthy schoolchildren, schizophrenia, psychological functions in healthy adults and geriatric patients) there is no adequate support from controlled trials in favor of vitamin supplementation.